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A Ce atom reaction with propene is carried out in a pulsed laser vaporization molecule beam source. Several Ce–hydrocarbon species formed by the C—H and C—C bond activation of propene are observed by time-of-flight mass spectrometry, and Ce(C3Hn) (n = 4 and 6) are characterized by mass-analyzed threshold ionization (MATI) spectroscopy and density functional theory, multiconfiguration, and relativistic quantum chemical calculations. The MATI spectrum of each species consists of two vibronic band systems, each with several vibronic bands. Ce(C3H6) is identified as an inserted species with Ce inserting into an allylic C—H bond of propene and Ce(C3H4) as a metallocycle through 1,2-vinylic dehydrogenation. Both species have a Cs structure with the Ce 4f16s1 ground valence electron configuration in the neutral molecule and the Ce 4f1 configuration in the singly charged ion. The two vibronic band systems observed for each species are attributed to the ionization of two pairs of the lowest spin–orbit coupled states with each pair being nearly degenerate. [ABSTRACT FROM AUTHOR]

In the present work, we report exploitation of spatial symmetry in calculations of ground state energy and analytic first derivatives of closed-shell molecules based on our previously developed coupled-cluster (CC) approach with spin-orbit coupling. Both time-reversal symmetry and spatial symmetry for D2h and its subgroups are exploited in the implementation. The symmetry of a certain spin case for the amplitude, intermediate, or density matrix is determined by the symmetry of the corresponding spin functions and the direct product decomposition method is employed in computations involving these quantities. The reduction in computational effort achieved through the use of spatial symmetry is larger than the order of the molecular single point group. Symmetry exploitation renders application of the CC approaches with spin-orbit coupling to larger closed-shell molecules containing heavy elements with high accuracy. [ABSTRACT FROM AUTHOR]

Metal-pyridine (metal=Li, Ca, and Sc) complexes are produced inlaser-vaporization molecular beams and studied by pulsed-field-ionization zero-electron-kinetic-energy (ZEKE) spectroscopy and theoretical calculations. Both σ and π structures are considered for the three complexes by theory, and preferred structures are determined by the combination of the ZEKE spectra and calculations. The Li and Ca complexes prefer a σ bonding mode, whereas the Sc complex favors a π mode. Adiabatic ionization energies and metal-ligand vibrational frequencies are determined from the ZEKE spectra. Metal-ligand bond dissociation energies of the neutral complexes are obtained from a thermodynamic cycle. The ionization energies follow the trend of Li-pyridine (32 460 cm-1)≤Ca-pyridine(39 043 cm-1)≤Sc-pyridine(42 816 cm-1), whereas the bond energies are in the order of Ca-pyridine (27.0 kJ mol-1)≤Li-pyridine(49.1 kJ mol-1)≤Sc-pyridine(110.6 kJ mol-1). The different bonding modes between the main group metals and transition element are discussed in terms of Sc 3d orbital involvement. The bond energy differences between the Li and Ca metals are explained by the number of valence s electrons and the size of the metal atoms. [ABSTRACT FROM AUTHOR]

Vibrational frequencies of three niobium normal modes of triniobium dicarbide neutral and cation have been determined from pulsed field ionization-zero electron kinetic energy photoelectron spectra. The niobium stretching mode has a frequency of 326 cm[SUP-1]in the neutral and 339 cm[SUP-1]in the ion. The two deformation modes have frequencies of 238 and 82 cm[SUP-1]in the neutral and a degenerate frequency of 258 cm[SUP-1]in the ion. The geometry of the triniobium dicarbide has been established by comparing the experimental spectra with theoretical calculations. The cluster has a trigonal bipyramid geometry with carbon atoms capping on each face of the metal frame. The cation cluster has D[SUB3h] symmetry whereas the neutral cluster has lower symmetry resulting from a Jahn-Teller distortion. A second low-lying structure with doubly bridging carbon atoms has been identified by the calculations but has not yet been observed. [ABSTRACT FROM AUTHOR]

The geometrical structures of the ground states of triniobium monoxide, Nb3O, and its cation, Nb3O+, have been determined by an experimental and theoretical study. Vibrationally resolved photoelectron spectra of an Nb3O cluster beam were obtained at 100 and 300 K using the pulsed field ionization-zero electron kinetic energy technique. The spectra were simulated by calculating multidimensional Franck–Condon factors using the geometries and harmonic vibrational frequencies obtained from density functional theory for the minimum energy structures of the ion and neutral molecule. The rather remarkable agreement between the experiment and the simulated spectra establishes that Nb3O and Nb3O+ have planar C2v structures with the oxygen atom bridging two niobium atoms. These are the most complex transition metal cluster structures to date to be characterized by gas phase spectroscopic techniques. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The technique of pulsed-field-ionization zero-kinetic-energy (PFI-ZEKE), photoelectron spectroscopy was employed to probe the electronic structure of the V+2 cation. Rotationally resolved PFI-ZEKE spectra of the V+2 ground state were obtained by two color excitation via the 700 nm A 3Πu←X 3Σ-g system. The observation of transitions from the A 3Π2u state to two spin–orbit components with Ω=1/2 and Ω=3/2, confirms that the cation ground state has 4Σg- symmetry, in accordance with previous experimental and theoretical work. Striking differences were observed in the rotational selection rules for the 4Σg-←A 3Π1u and the 4Σg-←A 3Π2u transitions. The adiabatic ionization potential of V2 was determined to be 51 271.14(50) cm-1. From an analysis of the rotational structure of the PFI-ZEKE spectra, the following molecular constants were determined for the 4Σg- state: r0=1.7347(24) Å, second order spin–orbit splitting, λ=5.248(17) cm-1, spin–rotation constant, γ=0.0097(87) cm-1, T0=51 282.20(50) cm-1 (1σ error bounds). © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Although it plays a critical role in the photophysics and catalysis of lanthanides, spin–orbit coupling of electrons on individual lanthanide atoms in small clusters is not well understood. The major objective of this work is to probe such coupling of the praseodymium (Pr) 4f and 6s electrons in Pr2O2 and Pr2O2+. The approach combines mass-analyzed threshold ionization spectroscopy and spin–orbit multiconfiguration second-order quasi-degenerate perturbation theory. The energies of six ionization transitions are precisely measured; the adiabatic ionization energy of the neutral cluster is 38 045 (5) cm−1. Most of the electronic states involved in these transitions are identified as spin–orbit coupled states consisting of two or more electron spins. The electron configurations of these states are 4f46s2 for the neutral cluster and 4f46s for the singly charged cation, both in planar rhombus-type structures. The spin–orbit splitting due to the coupling of the electrons on the separate Pr atoms is on the order of hundreds of wavenumbers. [ABSTRACT FROM AUTHOR]

Metal-mediated N–H and C–H bond activation of aliphatic amines is an effective strategy for synthesizing biologically important molecules. Ln (Ln = La and Ce) atom reactions with dimethylamine are carried out in a pulsed-laser vaporization supersonic molecular beam source. A series of dehydrogenation species are observed with time-of-flight mass spectrometry, and the dehydrogenated Ln-containing species in the formula Ln(CH2NCH3) are characterized by single-photon mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical calculations. The theoretical calculations include density functional theory for both Ln species and multiconfiguration self-consistent field and quasi-degenerate perturbation theory for the Ce species. The MATI spectrum of La(CH2NCH3) consists of a single vibronic band system, which is assigned to the ionization of the doublet ground state of N-methyl-lanthanaaziridine. The MATI spectrum of Ce(CH2NCH3) displays two vibronic band systems, which are attributed to the ionization of two-pair lowest-energy spin–orbit coupling states of N-methyl-ceraaziridine. Both metallaaziridines are three-membered metallacycles and formed by the thermodynamically and kinetically favorable concerted dehydrogenation of the amino group and one of the methyl groups. [ABSTRACT FROM AUTHOR]

Ln (Ln = La and Ce) atom reactions with methylamine are carried out in a pulsed-laser vaporization supersonic molecular beam source. A series of dehydrogenation species are observed with time-of-flight mass spectrometry, and the dehydrogenated Ln-containing species in the formula Ln(NCH3) are characterized by mass-analyzed threshold ionization (MATI) spectroscopy and density functional theory and multiconfiguration spin–orbit coupling computations. The MATI spectrum of La(NCH3) consists of two vibronic band systems that are assigned to the ionization of the 2A1 ground state of the C3v isomer La(N–CH3) and the 2A′ ground state of the Cs isomer La(NH–CH2). The MATI spectrum of Ce(NCH3) also displays two band systems, which are attributed to the ionization of the low-energy spin–orbit coupling states of the C3v isomer Ce(N–CH3). Ln(N–CH3) is formed by the concerted dehydrogenation of the amino group, while La(NH–CH2) is formed by the dehydrogenation of both amino and methyl groups. Ce(NH–CH2) is presumably formed in the reaction based on the computational predictions but not observed by the spectroscopic measurements. [ABSTRACT FROM AUTHOR]

Ce atom reactions with ethylene, 2-butene, and isobutene are carried out in a pulsed laser vaporization molecule beam source. Ce-containing species are observed with time-of-flight mass spectrometry, and Ce(C4H6) is characterized with mass-analyzed threshold ionization (MATI) spectroscopy and relativistic quantum chemical calculations. Two structural isomers are identified for Ce(C4H6): one is the tetrahedronlike Ce[C(CH2)3] in C3v symmetry and the other is the five-membered metallocyclic Ce(CH2CHCHCH2) in Cs. The MATI spectrum of the C3v isomer exhibits two vibronic band systems separated by 88 cm−1, while that of the Cs isomer displays three split by 60 and 101 cm−1. The multiple band systems are attributed to spin-orbit splitting and vibronic transitions involving metal-hydrocarbon and hydrocarbon-based vibrations. The splitting in the C3v isomer arises from interactions of two triplet and two singlet states at the lowest energies, while each splitting in the Cs isomer involves two triplets and a singlet. Although the Ce atom has ground electron configuration 4f15d16s2, Ce valence electron configurations in both isomers are 4f16s1 in the neutral ground state and 4f1 in the ion. The remaining Ce 5d electrons in the isolated atom are spin paired in molecular orbitals that are a bonding combination between Ce 5dπ and hydrocarbon π* orbitals. [ABSTRACT FROM AUTHOR]

Ln (Ln = La and Ce) atom reactions with ammonia are carried out in a pulsed laser vaporization supersonic molecular beam source. Lanthanide-containing species are observed with time-of-flight mass spectrometry, and LnNH molecules are characterized by mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical calculations. The theoretical calculations include density functional theory for both Ln species and a scalar relativity correction, electron correlation, and spin-orbit coupling for the Ce species. The MATI spectrum of LaNH exhibits a single vibronic band system with a strong origin band and two weak vibronic progressions, whereas the spectrum of CeNH displays two band systems separated by 75 cm−1 with each being like the LaNH spectrum. By comparing with the theoretical calculations, both LaNH and CeNH are identified as linear molecules with C∞v symmetry, and the two vibronic progressions are attributed to the excitations of Ln–N stretching and Ln–N–H bending modes in the ions. The additional band system observed for CeNH is due to the spin-orbit splitting from the interactions of triplet and singlet states. The ground valence electron configurations of LaNH and CeNH are La 6s1 and Ce 4f16s1, and the ionization of each species removes the Ln 6s1 electron. The remaining two electrons that are associated with the isolated Ln atoms or ions are in a doubly degenerate molecular orbital that is a bonding combination between Ln 5dπ and N pπ orbitals. [ABSTRACT FROM AUTHOR]

La atom reaction with isoprene is carried out in a laser-vaporization molecular beam source. The reaction yields an adduct as the major product and C—C cleaved and dehydrogenated species as the minor ones. La(C5H8), La(C2H2), and La(C3H4) are characterized with mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical computations. The MATI spectra of all three species exhibit a strong origin band and several weak vibronic bands corresponding to La-ligand stretch and ligand-based bend excitations. La(C5H8) is a five-membered metallacycle, whereas La(C2H2) and La(C3H4) are three-membered rings. All three metallacycles prefer a doublet ground state with a La 6s1-based valence electron configuration and a singlet ion. The five-membered metallacycle is formed through La addition and isoprene isomerization, whereas the two three-membered rings are produced by La addition and insertion, hydrogen migration, and carbon-carbon bond cleavage. [ABSTRACT FROM AUTHOR]

The precise ionization energy of praseodymium oxide (PrO) seeded in supersonic molecular beams is measured with mass-analyzed threshold ionization (MATI) spectroscopy. A total of 33 spin–orbit (SO) states of PrO and 23 SO states of PrO+ are predicted by second-order multiconfigurational quasi-degenerate perturbation (MCQDPT2) theory. Electronic transitions from four low-energy SO levels of the neutral molecule to the ground state of the singly charged cation are identified by combining the MATI spectroscopic measurements with the MCQDPT2 calculations. The precise ionization energy is used to reassess the ionization energies and the reaction enthalpies of the Pr + O → PrO+ + e− chemi-ionization reaction reported in the literature. An empirical formula that uses atomic electronic parameters is proposed to predict the ionization energies of lanthanide monoxides, and the empirical calculations match well with available precise experimental measurements. [ABSTRACT FROM AUTHOR]

The structural and bonding properties of the Pt2C2n− (n = 1–3) complexes have been investigated by mass-selected photoelectron velocity-map imaging spectroscopy with quantum chemical calculations. The adiabatic detachment energies and vertical detachment energies of Pt2C2n− have been obtained from the measured photoelectron imaging spectra. Theoretical results indicate that the lowest-energy isomers of Pt2C2n− (n = 1–3) possess linear chain-shaped configurations. The binding motif in the most stable isomer of Pt2C2− has a linear cumulenic structure with a Pt=C=C=Pt configuration, and the structural characteristic persists up to all the lowest-energy isomers of the Pt2C4− and Pt2C6− anions. The chemical bonding analyses indicate that the Pt2C2n− (n = 1–3) complexes have multicenter two-electron characteristics. [ABSTRACT FROM AUTHOR]

Vibronic spectra of lutetium oxide (LuO) seeded in supersonic molecule beams are investigated with mass-analyzed threshold ionization (MATI) spectroscopy and second-order multiconfigurational quasi-degenerate perturbation (MCQDPT2) theory. Six states of LuO and four states of LuO+ are located by the MCQDPT2 calculations, and an a3Π(LuO+) ← C2Σ+ (LuΟ) transition is observed by the MATI measurement. The vibronic spectra show abnormal vibrational intervals for both the neural and cation excited states, and the abnormality is attributed to vibrational perturbations induced by interactions with neighboring states. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons are model systems for studying the mechanisms of lithium storage in carbonaceous materials. In this work, Li complexes of naphthalene, pyrene, perylene, and coronene were synthesized in a supersonic metal-cluster beam source and studied by zero-electron-kinetic-energy (ZEKE) electron spectroscopy and density functional theory calculations. The adiabatic ionization energies of the neutral complexes and frequencies of up to nine vibrational modes in the singly charged cations were determined from the ZEKE spectra. The metal-ligand bond energies of the neutral complexes were obtained from a thermodynamic cycle. Preferred Li/Li+ binding sites with the aromatic molecules were determined by comparing the measured spectra with theoretical calculations. Li and Li+ prefer the ring-over binding to the benzene ring with a higher π-electron content and aromaticity. Although the ionization energies of the Li complexes show no clear correlation with the size of the aromatic molecules, the metal-ligand bond energies increase with the extension of the π-electron network up to perylene, then decrease from perylene to coronene. The trends in the ionization and metal-ligand bond dissociation energies of the complexes are discussed in terms of the orbital energies, local quadrupole moments, and polarizabilities of the free ligands and the charge transfer between the metal atom and aromatic molecules. [ABSTRACT FROM AUTHOR]

Copper-diammonia, Cu(NH3)2, and its deuterated species, Cu(ND3)2, are produced in supersonic molecular beams and studied by pulsed-field ionization zero electron kinetic energy photoelectron spectroscopy and ab initio calculations. Structural isomers with a copper atom binding to an ammonia dimer or two ammonia molecules are obtained by the calculations. By comparing the experimental measurements to the theoretical calculations, the neutral and ionic forms of copper-diammonia are determined to be in a doubly bound linear conformation in their ground electronic states. The adiabatic ionization potentials of Cu(NH3)2 and Cu(ND3)2 are measured as 29 532 (5) and 29 313 (5) cm-1, respectively. The metal-ligand symmetric stretching frequencies are measured to be 436 cm-1 for Cu+–(NH3)2 and 398 cm-1 for Cu+–(ND3)2, and the metal-ligand bending frequencies 75/139 cm-1 for Cu/Cu+–(NH3)2 and 70/125 cm-1 for Cu/Cu+–(ND3)2. Moreover, the dissociation energy of Cu(NH3)2→CuNH3+NH3 is determined to be 11(3) kcal mol-1 through a thermodynamic relationship. [ABSTRACT FROM AUTHOR]

The yttrium complexes with one and two dimethyl ethers and their deuterated derivatives are prepared with laser vaporization molecular beam techniques, identified with photoionization time-of-flight mass spectrometry, and investigated with pulsed-field-ionization zero-electronkinetic-energy (ZEKE) photoelectron spectroscopy and ab initio calculations. Adiabatic ionization potentials and yttrium-oxygen stretch and ether-based vibrations are measured for the 1:1 and 1:2 complexes. Fermi interactions are observed from the ZEKE spectra of the 1:1 species. The ground electronic states of the monoligand complexes are determined to be [SUP2]A[SUB2] for the neutral and [SUP1]A[SUB1] for the singly charged positive ion, both in C[SUB2v] symmetry, with yttrium binding to oxygen. The coordination of a second ether forms a diligand complex with a linear oxygen-yttrium-oxygen configuration. This is the first electronic-vibrational spectroscopic study of yttrium-polyatomic molecule complexes and weakly bound metal complexes with two or more polyatomic molecules. [ABSTRACT FROM AUTHOR]

Aluminum-trimethylphosphine and trimethylarsine have been prepared by pulsed laser vaporization. Their electronic spectra have been obtained for the first time, using pulsed field ionization zero electron kinetic energy (ZEKE) photoelectron spectroscopy. The ZEKE spectra reveal the information about adiabatic ionization energies, intermolecular and ligand vibrations, and charge effects on molecular geometries. In coordination with the experimental measurements, density functional theory has been used to calculate equilibrium geometries, vibrational frequencies, and bond dissociation energies for the neutral and ionic complexes. The calculations predict that ionization causes the most significant geometry changes in the Al–P–C or Al–As–C angles, in agreement with the experimental observations. The aluminum ion and atom bind phosphorus more strongly than arsenic in these species. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Upconverting nanoparticles (UCNPs) composed of NaYF4 and doped with photoactive Yb3+ and Er3+ (NaYF4:Yb/Er) are highly desirable for many biological applications, but obtaining stable dispersions of UCNPs is challenging. Traditional synthetic methods often use complicated synthetic steps, produce toxic side products, and require post modifications to make UCNPs more dispersible in aqueous solutions. In this study, we demonstrate that laser ablation in liquid (LAL) is a novel approach to synthesize water-dispersible and -stable UCNPs with advantages of particle-size tuning, in situ coating of UCNPs with capping agents, no use of toxic or high boiling point solvents, and short reaction times. NaYF4:Yb/Er UCNPs were produced through LAL of annealed targets using water as the liquid, and their compositions and properties were investigated at a laser fluence of 0.57 J cm−2–6.22 J cm−2 by direct capping with citric acid and ethylene glycol and by comparing with the UCNPs prepared from the traditional hydrothermal method. Low laser fluences produced polydisperse particles consisting of no photoactive species through a thermal evaporation mechanism, while high laser fluences generated UCNPs with more uniform morphologies and compositions similar to the target material by an explosive ejection mechanism. The inclusion of capping agents during LAL allowed for direct coating of the UCNP surface without the need of post modifications, and the concentrations of capping agents affected the UCNP photoluminescence lifetimes. As compared to the hydrothermal method, the LAL-prepared samples showed better size control and no degradation of the capping agents. [ABSTRACT FROM AUTHOR]

La atom reactions with 1-pentene and 2-pentene are carried out in a laser-vaporization molecular beam source. The two reactions yield the same metal-hydrocarbon products from the dehydrogenation and carbon–carbon bond cleavage of the pentene molecules. The dehydrogenated species La(C5H8) is the major product, whereas the carbon–carbon bond cleaved species La(C2H2) and La(C3H4) are the minor ones. La(C10H18) is also observed and is presumably formed by La(C5H8) addition to a second pentene molecule. La(C5H8) and La(C2H2) are characterized with mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical computations. The MATI spectra of each species from the two reactions exhibit the same transitions. Adiabatic ionization energies and metal-ligand stretching frequencies are determined for the two species, and additional methyl bending and torsional frequencies are measured for the larger one. Five possible isomers are considered for La(C5H8), and a C1 metallacyclopentene (Iso A) is identified as the most possible isomer. La(C2H2) is confirmed to be a C2v metallacyclopropene. The ground electronic state of each species is a doublet with a La 6s1-based electron configuration, and ionization yields a singlet state. The formation of the lanthanacyclopentene includes La addition to the C=C double bond, La insertion into two C(sp3)—H bonds, and concerted dehydrogenation. For the 2-pentene reaction, the formation of the five-membered ring may also involve 2-pentene to 1-pentene isomerization. In addition to the metal addition and insertion, the formation of the three-membered metallacycle from 1-pentene includes C(sp3)—C(sp3) bond breakage and hydrogen migration from La to C(sp3), whereas its formation from 2-pentene may involve the ligand isomerization. [ABSTRACT FROM AUTHOR]

La atom reactions with 1-butene, 2-butene, and isobutene are carried out in a laser-vaporization molecular beam source. The three reactions yield the same La-hydrocarbon products from the dehydrogenation and carbon-carbon bond cleavage and coupling of the butenes. The dehydrogenated species La(C4H6) is the major product, which is characterized with mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical computations. The MATI spectrum of La(C4H6) produced from the La+1-butene reaction exhibits two band systems, whereas the MATI spectra produced from the La+2-butene and isobutene reactions display only a single band system. Each of these spectra shows a strong origin band and several vibrational progressions. The two band systems from the spectrum of the 1-butene reaction are assigned to the ionization of two isomers: La[C(CH2)3] (Iso A) and La(CH2CHCHCH2) (Iso B), and the single band system from the spectra of the 2-butene and isobutene reactions is attributed to Iso B and Iso A, respectively. The ground electronic states are 2A1 (C3v) for Iso A and 2A′ (Cs) for Iso B. The ionization of the doublet state of each isomer removes a La 6s-based electron and leads to the 1A1 ion of Iso A and the 1A′ ion of Iso B. The formation of both isomers consists of La addition to the C=C double bond, La insertion into two C(sp3)—H bonds, and H2 elimination. In addition to these steps, the formation of Iso A from the La+1-butene reaction may involve the isomerization of 1-butene to isobutene prior to the C—H bond activation, whereas the formation of Iso B from the La+trans-2-butene reaction may include the trans- to cis-butene isomerization after the C—H bond activation. [ABSTRACT FROM AUTHOR]

Group 3 metal-aniline complexes, M(aniline) (M = Sc, Y, and La), are produced in a pulsed laser-vaporization molecular beam source, identified by photoionization time-of-flight mass spectrometry, and investigated by pulsed-field ionization zero electron kinetic energy (ZEKE) spectroscopy and quantum chemical calculations. Adiabatic ionization energies and several low-frequency vibrational modes are measured for the first time from the ZEKE spectra. Metal binding sites and electronic states are determined by combining the ZEKE measurements with the theoretical calculations. The ionization energies of the complexes decrease down the metal group. An out-of-plane ring deformation mode coupled with an asymmetric metal-carbon stretch is considerably anharmonic. Although aniline has various possible sites for metal coordination, the preferred site is the phenyl ring. The metal binding with the phenyl ring yields syn and anti conformers with the metal atom and amino hydrogens on the same and opposite sides of the ring, respectively. The anti conformer is determined to be the spectral carrier. The ground electronic state of the anti conformer of each neutral complex is a doublet with a metal-based electron configuration of nd2(n + 1)s1, and the ground electronic state of each ion is a singlet with a metal-based electron configuration of nd2. The formation of the neutral complexes requires the nd2(n + 1)s1 ← nd1(n + 1)s2 electron excitation in the metal atoms. [ABSTRACT FROM AUTHOR]

M3O4 (M = Sc, Y, and La) were produced in a pulsed laser-vaporization molecular beam source and studied by mass-analyzed threshold ionization (MATI) spectroscopy and electronic structure calculations. Adiabatic ionization energies (AIEs) of the neutral clusters and vibrational frequencies of the cations were measured accurately for the first time from the MATI spectra. Five possible structural isomers of M3O4 were considered in the calculations and spectral analysis. A cage-like structure in C3v point group was identified as the most stable one. The structure is formed by fusing three M2O2 fragments together, each sharing two O-M bonds with others. The ground electronic state of the neutral clusters is 2A1 with the unpaired electron being largely a metal-based s character. Ionization of the 2A1 state yields a 1A1 ion state in a similar geometry to the neutral cluster. The AIEs of the clusters are 4.4556 (6), 4.0586(6), and 3.4750(6) eV for M = Sc, Y, and La, respectively. The observed vibrational modes of the cations include metal-oxygen stretching, metal triangle breathing, and oxygen-metal-oxygen rocking in the frequency range of 200-800 cm-1. [ABSTRACT FROM AUTHOR]

Neodymium (Nd) complexes of benzene and naphthalene were synthesized in a laser-ablation supersonic molecular beam source. High-resolution electron spectra of these complexes were obtained using pulsed-field ionization zero electron kinetic energy (ZEKE) spectroscopy. Second-order Mo\ller-Plesset perturbation calculations were employed to aid spectral and electronic-state assignments. The adiabatic ionization energies were measured to be 38 081 (5) cm-1 for Nd(benzene) and 37 815 (5) cm-1 for Nd(naphthalene). For the Nd(benzene) complex, the observed frequencies of 831 and 286 cm-1 were assigned to C-H out-of-plane bending and Nd+-C6H6 stretching modes in the 6A1 ion state and 256 cm-1 to the Nd-C6H6 stretching mode in the 7A1 neutral state. To confirm these assignments, the ZEKE spectrum of the deuterated species was recorded, and the corresponding vibrational frequencies were measured to be 710 and 277 cm-1 in the ion state and 236 cm-1 in the neutral state. For the Nd(naphthalene) complex, the observed vibrational modes were C10H8 bending (394 cm-1), Nd+-C10H8 stretching (286 and 271 cm-1), Nd+-C10H8 bending (80 cm-1), and C10H8 twisting (105 cm-1) in the 6A′ ion state and metal-ligand bending (60 cm-1) and ligand twisting (55 cm-1) in the 7A′ neutral state. The formation of the ground state of the Nd(benzene) complex requires 4f → 5d and 6s → 5d electron excitation of the Nd atom, whereas the formation of the ground state of Nd(naphthalene) involves the 6s → 5d electron promotion. [ABSTRACT FROM AUTHOR]

Lanthanum dimer (La2) was studied by mass-analyzed threshold ionization (MATI) spectroscopy and a series of multi-configuration ab initio calculations. The MATI spectrum exhibits three band systems originating from ionization of the neutral ground electronic state, and each system shows vibrational frequencies of the neutral molecule and singly charged cation. The three ionization processes are La2+ (a2∑g+) ← La2 (X1∑g+), La2+ (b2Π3/2, u) ← La2 (X1∑g+), and La2+ (b2Π1/2, u) ← La2 (X1∑g+), with the ionization energies of 39 046, 40 314, and 40 864 cm-1, respectively. The vibrational frequency of the X1Σg+ state is 207 cm-1, and those of the a2Σg+, b2Π3/2, u and b2Π1/2, u are 235.7, 242.2, and 240 cm-1. While X1Σg+ is the ground state of the neutral molecule, a2Σg+ and b2Πu are calculated to be the excited states of the cation. The spin-orbit splitting in the b2Πu ion is 550 cm-1. An X4Σg- state of La2+ was predicted by theory, but not observed by the experiment. The determination of a singlet ground state of La2 shows that lanthanum behaves differently from scandium and yttrium. [ABSTRACT FROM AUTHOR]

Al-thymine (Al–C4H3N2O2CH3) is produced by laser vaporization of a rod made of Al and thymine powders in a molecular beam and studied by single-photon pulsed-field ionization-zero electron kinetic energy (ZEKE) photoelectron and IR-UV resonant two-photon ionization spectroscopy and density functional theory calculations. The ZEKE experiment determines the adiabatic ionization energy of the neutral complex and 22 vibrational modes for the corresponding ion with frequencies below 2000 cm-1. The IR-UV photoionization experiment measures two N–H and three C–H stretches for the neutral species. The theoretical calculations predict a number of low-energy isomers with Al binding to single oxygen or adjacent oxygen and nitrogen atoms of thymine. Among these isomers, the structure with Al binding to the O4 atom of the diketo tautomer is predicted to be the most stable one by the theory and is probed by both ZEKE and IR-UV measurements. This work presents the first application of the IR-UV resonant ionization to metal-organic molecule systems. Like ZEKE spectroscopy, the IR-UV photoionization technique is sensitive for identifying isomeric structures of metal association complexes. [ABSTRACT FROM AUTHOR]

The ethylenediamine (en) complexes of Al, Ga, and In atoms were prepared in laser-vaporization supersonic molecular beams and studied with pulsed field ionization zero electron kinetic energy photoelectron spectroscopy and density functional theory. Several conformers of each metal complex are obtained by B3LYP calculations, and a five-membered cyclic structure is identified by combining the experimental measurements and theoretical calculations. Adiabatic ionization potentials, vibrational frequencies, and bond dissociation energies are determined for the ring structure. The ionization potentials of the Al, Ga, and In species are measured to be 32 784 (5), 33 324 (5), and 33 637 (7) cm-1, respectively, and metal-ligand dissociation energies of the ionic and neutral complexes are calculated to be 60.2/16.2 (Al+/Al), 55.5/13.0 (Ga+/Ga), and 50.0/11.4 (In+/In) kcal mol-1. Metal-ligand stretch and bend as well as a number of ligand-based vibrations are measured. Harmonic frequencies and anharmonicities of the M+-N (M=Al,Ga,In) stretch are determined for all three M+-en ions and the C-C-N bend of Ga+-en and In+-en. In comparison to monodentate methylamine, the bidentate binding of ethylenediamine leads to a significantly lower ionization potential and higher metal-ligand bond strength of the metal complexes. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The copper complexes were produced in pulsed laser vaporization molecular beams and investigated by pulsed-field ionization zero electron kinetic energy (ZEKE) spectroscopy and second-order Møller–Plesset (MP2) perturbation and hybrid B3LYP density functional theory calculations. The ground electronic states of Cu–X(CH[sub 3])[sub 3] and Cu[sup +]–X(CH[sub 3])[sub 3] (X=N,P,As) are [sup 2]A[sub 1] and [sup 1]A[sub 1], respectively, both with C[sub 3v] symmetry. From the ZEKE spectra, the adiabatic ionization potentials of the neutral molecules are determined to be 44 730, 41 508, and 42 324 cm-1, and the Cu[sup +]/Cu–X stretching frequencies are 268/199, 214/187, and 188/155 cm-1 for X=N, P, and As, respectively. The degenerate Cu[sup +]/Cu–P–C and Cu[sup +]/Cu–As–C bending frequencies are measured to be 146/83 and 118/52 cm-1, while the Cu[sup +]/Cu–N–C mode was not observed. In addition, the CH[sub 3] wag, X–C stretching, and XC[sub 3] umbrella modes are also measured for the phosphine and arsine complexes. From the MP2 theory, the dissociation energies of the Cu[sup +] and Cu complexes are estimated to be 59/12, 70/15, and 65/11 kcal mol-1 down the X group. Both MP2 and B3LYP predictions of ionic vibrational frequencies compare well with the spectroscopic values, but the B3LYP calculations of neutral low frequency modes are less satisfactory. On the other hand, the B3LYP calculations yield better ionization potentials than the MP2 methods for these molecules. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Aluminum–methylamine complexes are produced in pulsed molecular beams. Their electronic spectra are obtained using threshold photoionization and zero-electron-kinetic-energy photoelectron spectroscopies and interpreted using density functional and ab initio calculations. The photoelectron spectra reveal ground electronic states and intermolecular and ligand-based vibrations of Al–NH[sub n](CH[sub 3])[sub 3-n] and Al[sup +]–NH[sub n](CH[sub 3])[sub 3-n] (n=0–2), adiabatic ionization energies of Al–NH[sub n](CH[sub 3])[sub 3-n], and a low-lying excited electronic state of Al–NH[sub 2]CH[sub 3]. In addition, the spectroscopic measurements and theoretical calculations show strong methyl substitution effects on the ionization energies and metal–ligand binding. Striking spectral differences are discovered between these aluminum complexes and previously studied gallium and indium analogues. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The gallium complexes were produced in pulsed molecular beams and studied with zero electron kinetic energy (ZEKE) photoelectron spectroscopy. Intermolecular vibrational frequencies and adiabatic ionization potentials (IPs) were obtained from ZEKE spectra. Ground electronic states were identified by combining the ZEKE spectra with quantum chemical and Franck–Condon calculations. Ga–NH[sub 3] has an IP of 40 135 cm-1 and metal-ligand stretching frequencies of 270 cm-1 (ω[sub s][sup +]) in the ion and 161 cm-1 (ν[sub s]) in the neutral. The IP of Ga–NH[sub 2]CH[sub 3] is 39 330 cm-1, and the vibrational frequencies are 93 cm-1 (ν[sub b]) for the Ga–N–C bending, 124 cm-1 (ω[sub b][sup +]) for the Ga[sup +]–N–C bending, and 299 cm-1 (ω[sub s][sup +]) for the Ga[sup +]–N stretching. The strength of the gallium–methylamine binding is stronger than that of the gallium–ammonia. The ground state of Ga–NH[sub 3] is [sup 2]A[sup ′](C[sub s]) and that of Ga[sup +]–NH[sub 3] is [sup 1]A[sub 1](C[sub 3v]). In contrast, Ga–NH[sub 2]CH[sub 3] has two doublets, [sup 2]A[sup ′] and [sup 2]A[sup ″](C[sub s]), with virtually the same energies, whereas Ga[sup +]–NH[sub 2]CH[sub 3] has a [sup 1]A[sup ′](C[sub s]) ground state. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Cerium, praseodymium, and neodymium complexes of 1,3,5,7-cyclooctatetraene (COT) complexes were produced in a laser-vaporization metal cluster source and studied by pulsed-field ionization zero electron kinetic energy spectroscopy and quantum chemical calculations. The computations included the second-order Mo\ller-Plesset perturbation theory, the coupled cluster method with single, double, and perturbative triple excitations, and the state-average complete active space self-consistent field method. The spectrum of each complex exhibits multiple band systems and is assigned to ionization of several low-energy electronic states of the neutral complex. This observation is different from previous studies of M(COT) (M = Sc, Y, La, and Gd), for which a single band system was observed. The presence of the multiple low-energy electronic states is caused by the splitting of the partially filled lanthanide 4f orbitals in the ligand field, and the number of the low-energy states increases rapidly with increasing number of the metal 4f electrons. On the other hand, the 4f electrons have a small effect on the geometries and vibrational frequencies of these lanthanide complexes. [ABSTRACT FROM AUTHOR]

LaO2 was produced in a pulsed laser-vaporization molecular beam source and studied by mass-analyzed threshold ionization (MATI) spectroscopy and ab initio electronic structure calculations. The calculations included density functional theory, second-order perturbation theory, coupled cluster theory, and complete active space self-consistent field methods. The adiabatic ionization energy of the molecule and vibrational frequencies of the molecule and its cation were measured accurately for the first time from the MATI spectrum. Numerous ionization processes of lanthanum dioxide, peroxide, and superoxide were considered; the 3B2 ← 4B2 electronic transition of the dioxide was assigned upon comparison with the observed spectrum. The ionization energy and O-La-O bending frequency of the 4B2 neutral state are 4.9760 (6) eV and 92 cm-1, respectively. The La-O stretching and O-La-O bending frequencies of the 3B2 cationic state are 656 and 122 cm-1, respectively. The 4B2 state is formed by two electron transfer from lanthanum to oxygen atoms, and the 3B2 state is produced by the further removal of a lanthanum 6s-based electron. [ABSTRACT FROM AUTHOR]

Monobenzene complexes of yttrium (Y), lanthanum (La), and lutetium (Lu), M(C6H6) (M = Y, La, and Lu), were prepared in a laser-vaporization supersonic molecular beam source and studied by pulsed-field ionization zero electron kinetic energy (ZEKE) spectroscopy and ab initio calculations. The calculations included the second-order perturbation, the coupled cluster with single, double, and perturbative triple excitation, and the complete active space self-consistent field methods. Adiabatic ionization energies and metal-benzene stretching frequencies of these complexes were measured for the first time from the ZEKE spectra. Electronic states of the neutral and ion complexes and benzene ring deformation were determined by combining the spectroscopic measurements with the theoretical calculations. The ionization energies of M(C6H6) are 5.0908 (6), 4.5651 (6), and 5.5106 (6) eV, and the metal-ligand stretching frequencies of [M(C6H6)]+ are 328, 295, and 270 cm-1 for M = Y, La, and Lu, respectively. The ground states of M(C6H6) and [M(C6H6)]+ are 2A1 and 1A1, respectively, and their molecular structures are in C2v point group with a bent benzene ring. The deformation of the benzene ring upon metal coordination is caused by the pseudo Jahn-Teller interaction of (12E2+12A1+22E2) x e2 at C6v symmetry. In addition, the study shows that spectroscopic behaviors of Y(C6H6) and La(C6H6) are similar to each other, but different from that of Lu(C6H6). [ABSTRACT FROM AUTHOR]

Single-photon pulsed field ionization-zero electron kinetic energy photoelectron spectroscopy has been used to study the indium–methylamine complexes. The photoelectron spectra have been assigned using density functional theory and Franck–Condon calculations. The spectral assignments identify the symmetric In[sup +]–N stretch mode for In[sup +]–NH[sub 2]CH[sub 3] (259 cm-1), In[sup +]–NH(CH[sub 3])[sub 2] (200 cm-1), and In[sup +]–N(CH[sub 3])[sub 3] (158 cm-1); In–N stretch for In–N(CH[sub 3])[sub 3] (110 cm-1); In[sup +]–N–C bend for In[sup +]–NH[sub 2]CH[sub 3] (110 cm-1) and In[sup +]–NH(CH[sub 3])[sub 2] (120 cm-1); In–N–C bend for In–NH[sub 2]CH[sub 3] (91 cm-1) and In–NH(CH[sub 3])[sub 2] (106 cm-1); and In[sup +]–N–H bend for In[sup +]–NH(CH[sub 3])[sub 2] (324 cm-1). Methyl substitutions for hydrogen atoms greatly influence the indium–nitrogen stretch forces and ionization potentials of the complexes. The indium–amine binding in these complexes includes orbital interaction and electrostatic forces. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]